1. Field of the Invention
The present invention relates to a liquid discharging method, a liquid discharge head and a recording apparatus using such a liquid discharge head, in which desired liquid is discharged by generating a bubble by thermal energy, and more particularly, it relates to a liquid discharge head using a movable separation diaphragm displaced by utilizing generation of a bubble.
Incidentally, a term xe2x80x9crecordingxe2x80x9d in this specification means not only to form a desired image such as character or figure on a recording medium, but also to form a meaningless image such as pattern on a recording medium.
2. Related Background Art
Conventionally, in recording apparatuses such as printers, an ink jet recording method, i.e., a so-called bubble jet recording method in which a bubble is generated by applying energy such as thermal energy to liquid ink in a flow path and the ink is discharged from a discharge port by an acting force generated by abrupt change in volume due to generation of the bubble thereby to adhere the discharged ink to a recording medium to form an image is well known.
As disclosed in U.S. Pat. No. 4,723,129, generally, the recording apparatus using such a bubble jet recording method comprises discharge ports for discharging ink, flow paths communicated with the discharge ports, and electrical/thermal converters as energy generating means for discharging the ink in the flow path(s).
According to such a recording method, since a high quality image can be recorded at a high speed with low noise and the discharge ports can be arranged with high density in a head performing this method, there can be provided many excellent advantages that a recorded image having high resolving power can be obtained by a compact apparatus, a color image can easily be obtained and the like. Thus, the bubble jet recording method has recently been used in many office equipments such as printers, copying machines, facsimiles and the like and has also been applied to industrial systems such as a print device.
As the bubble jet technique is used in wide technical fields, the following requests have recently been made.
A driving condition for providing a liquid discharging method capable of effecting good ink discharge on the basis of high speed ink discharge and stable generation of the bubble in order to obtain the high quality image has been proposed or an improved flow path configuration for obtaining a liquid discharge head having a high speed filling ability for re-filling or replenishing the liquid into the flow path for compensating the discharged liquid in consideration of high speed recording has been proposed.
Other than such heads, as disclosed in Japanese Patent Application Laid-open No. 6-31918, in consideration of a back wave (pressure directing a direction opposite to a direction toward the discharge port) generated by the generation of the bubble, a structure for preventing the back wave leading to loss energy at the discharge port has been proposed. In this proposed technique, a triangular portion of a triangular plate member is opposed to a heater for generating the bubble. In this technique, the back wave is temporarily and slightly suppressed by the plate member. However, since a relationship between the growth of the bubble and the triangular portion is not described at all and there is no such idea, this technique causes the following problems.
That is to say, in this technique, since the heater is located on a bottom of a recess not to be communicated with the discharge port straightly, a shape of a liquid droplet is not stabilized, and, since the growth of the bubble is permitted around an apex of the triangle, the bubble is grown from one side of the triangular plate member to the entire opposite side, with the result that the normal growth of the bubble is completed in the liquid as if there is no plate member. Accordingly, the grown bubble has no relationship to the plate member at all. Conversely, since the entire plate member is enclosed by the bubble, upon contraction of the bubble, the re-fill of the liquid to the heater located in the recess generates turbulent flow, with the result that small bubbles are trapped in the recess, thereby worsening the principle itself for effecting the liquid discharge on the basis of the growth of the bubble.
European Patent Appliction No. 0 436 047 A1 discloses a technique in which a first valve disposed between a discharge port and a bubble generation portion to block communication therebetween and a second valve disposed in the bubble generating portion and an ink supplying portion to completely block communication therebetween are opened and closed alternately (FIGS. 4 to 9 in EP 436047A1). However, in this technique, since these three chambers are partitioned to two chambers, upon discharging, the ink droplet creates a long ink tail to thereby generate many satellite dots in comparison with the normal technique for effecting bubble growth, bubble contraction and bubble extinction (it is guessed that the effect of retarding the meniscus due to bubble extinction cannot be utilized). Further, upon refilling, although the liquid is supplied to the bubble generating portion as a result of the bubble extinction, since the liquid cannot be supplied to the vicinity of the discharge port until the next bubble is generated, not only dispersion in discharged liquid droplets becomes great but also discharge response frequency becomes very small, and, thus, this technique cannot be put to a practical use.
On the other hand, unlike the above technique, the applicant has proposed many techniques in which a movable member (plate-shaped member having a free end disposed near a discharge port and at a downstream side of a fulcrum) contributing to effective discharge of a liquid droplet is used. Among them, Japanese Patent Application Laid-open No. 9-48127 discloses a technique in which an upper limit of displacement of the movable member is regulated to prevent the disturbance of performance of the movable member. Further, Japanese Patent Application Laid-open No. 9-323420 discloses a technique in which a position of a common liquid chamber located at an upstream side of the movable member is shifted toward the free end of the movable member, i.e., toward the downstream direction to enhance the re-filling ability by utilizing the advantage of the movable member. Since these techniques adopt a construction in which the grown bubble is released at once toward the discharge port from a condition that the bubble is temporarily constrained by the movable member, a relationship between the entire bubble and elements associated with the formation of the liquid droplet was not noticed.
In the next step, Japanese Patent Application Laid-open No. 10-24588 discloses a technique in which a part of a bubble generating area is released from the movable member in consideration of growth of the bubble due to pressure wave (acoustic wave) propagation as a factor associated with the liquid discharging. However, also in this technique, since only the growth of the bubble in the liquid discharging is noticed, a relationship between the entire bubble and elements associated with the formation of the liquid droplet was not noticed.
In the past, although the fact that a forward part (edge shooter type) of a bubble generated by film boiling affects a great influence upon the discharging was well known, the fact that such a part is caused to contribute to the formation of the discharge liquid droplet more effectively was not noticed, and the inventors have investigated to analyze such facts.
Further, the inventors noticed a relationship between the displacement of the movable member and the generated bubble and found the following effective technique.
Such a technique regulates the displacement of the free end of the movable member with respect to the growing bubble by a stopper. By regulating the displacement of the movable member by means of the stopper, the growth of the bubble toward the upstream direction is regulated, with the result that energy for discharging the liquid is efficiently transmitted toward the downstream side, i.e., toward the discharge port.
In such investigation step, it was found that the bubble sometimes moves around the tip end of the movable member having the free end capable of being displaced in response to the growth of the bubble under a certain condition during the displacement of the movable member. In the technical analysis, the following phenomenon was ascertained.
That is to say, as the bubble for discharging the liquid droplet grows and the movable member is displaced upwardly, the displacement of the movable member cannot follow the growth of the bubble, with the result that the grown bubble tries to ride on the upper surface of the movable member. However, it was observed that, under a certain condition, for example, in a condition that the resistance of a flow path at the liquid supply side is very small to easily shift the liquid toward the liquid supply side, as the liquid is shifted rearwardly of the nozzle flow path due to the displacement of the movable member, the bubble tends to travel rearward of the nozzle flow path.
When the flow of the liquid toward the rearward of the nozzle flow path is caused during the displacement of the movable member, it was found that the effect of the movable member for efficiently directing the discharge energy generated by the growth of the bubble is sometimes worsened.
To avoid this, the inventors found a flow path structure of a liquid discharge head utilizing a movable member having a free end in which liquid flow toward the rear of the flow path and entering of the bubble into the rear of the flow path are prevented, thereby enhancing the discharging efficiency forward of the nozzle and stabilizing quick return of the meniscus of the re-fill liquid during re-filling.
An object of the present invention is to provide a liquid discharging method, a liquid discharge head and a recording apparatus using such a liquid discharge head, in which liquid discharge energy generated by a bubble is efficiently transmitted to the liquid and the liquid is stably discharged.
To achieve the above object, in a liquid discharging method according to the present invention, there are provided a heat generating body (member) for generating thermal energy for generating a bubble in liquid, a discharge port for discharging the liquid, a flow path communicated with the discharge port and having a bubble generating area for generating the bubble in the liquid, a movable member having a free end and capable of being displaced as the bubble grows, and a regulating portion for regulating a displacement amount of the movable member, and the flow path is formed by joining a substantially flat substrate including the heat generating body and the movable member to a top plate opposed to the substrate and including the regulating portion and the liquid is discharged from the discharge port by energy generated by generation of the bubble. The liquid discharging method is characterized in that when both a volume change ratio of the bubble and a displacement volume change ratio of the movable member tend to increase, the displacement of the movable member is regulated by the regulating portion.
As mentioned above, in the liquid discharging method according to the present invention, since the displacement of the movable member is regulated by the regulating portion when both the volume change ratio of the bubble and the displacement volume change ratio of the movable member tend to increase, the shifting movement of the liquid toward an upstream side caused when the bubble is generated can be stopped.
A liquid discharge head according to the present invention comprises a heat generating body for generating thermal energy for generating a bubble in liquid, a discharge port for discharging the liquid, a flow path communicated with the discharge port and having a bubble generating area for generating the bubble in the liquid, a movable member having a free end and capable of being displaced as the bubble grows, and a regulating portion for regulating a displacement amount of the movable member, and the flow path is formed by joining a substantially flat substrate including the heat generating body and the movable member to a top plate opposed to the substrate and including the regulating portion and the liquid is discharged from the discharge port by energy generated by generation of the bubble. The liquid discharge head is characterized in that protruded height from a wall surface of the top plate defining an upper wall of the flow path to a tip end of the regulating portion is 20 xcexcm or more, and a first clearance within the flow path formed by the movable member and the regulating portion in an initial condition that the bubble is not generated is 25 xcexcm or less.
In the liquid discharge head having the above-mentioned arrangement, since the height of the regulating portion is 20 xcexcm or more and the first clearance within the flow path formed by the movable member and the regulating portion in the initial condition that the bubble is not generated is 25 xcexcm or less, when the movable member is displaced toward the top plate by growth of the bubble, the movable member is positively contacted with the regulating portion, thereby positively regulating the displacement amount of the movable member mechanically. Further, by selecting the height of the regulating portion and the first clearance within the flow path formed by the movable member and the regulating portion to the above-mentioned dimensional relationship, when the bubble is extinguished and the movable member contacted with the regulating portion is separated from the regulating portion and displaced toward the substrate, the influence of the regulating portion and the movable member upon flow of the liquid toward the discharge port can be reduced, thereby realizing the smooth liquid re-filling.
The regulating portion of the liquid discharge head according to the present invention may have a tip end regulating portion formed at a position opposed to the free end of the movable member and further may have side regulating portions located aside the bubble generating portion and formed at positions opposed to both lateral sides of the movable member. In this case, since the movable member displaced toward the top plate by the growth of the bubble is contacted with the tip end regulating portion and the side regulating portions, the bubble trying to go round from both lateral sides of the movable member toward the upstream side can be suppressed, thereby promoting the growth of the bubble toward the discharge port.
Further, a second clearance within the flow path formed by a lower surface of the movable member and the substrate in the initial condition that the bubble is not generated may be 5 xcexcm or more, and a thickness of the movable member may be about 5 xcexcm, and a distance between a wall surface of the substrate constituting a lower wall surface of the flow path and the upper wall surfacexe2x80x94which distance defines a height of the flow path in the bubble generating areaxe2x80x94may be about 55 xcexcm.
Further, the first clearance may be 10 xcexcm or more, and, when the protruded height is 30 xcexcm or more, the first clearance may be 15 xcexcm or less.
Further, the movable member may have a projection protruding from the lower surface toward the substrate. In this case, a third clearance within the flow path formed by the projection and the substrate in the initial condition that the bubble is not generated may be about 5 xcexcm, and, when the protruded height is about 20 xcexcm, the first clearance may be within a range from 10 xcexcm to 15 xcexcm, and the sum of the first clearance and the second clearance within the flow path formed by the lower surface of the movable member and the substrate may be about 30 xcexcm. By providing the projection on the lower surface of the movable member in this way, the growth of the bubble toward the upstream side can be regulated and the growth of the bubble toward the downstream side can be promoted. Further, when the bubble is extinguished and the movable member is displaced toward the substrate, even if the movable member is overshot by exceeding the position in the initial condition, the damage of the free end of the movable member or the substrate due to the contact between the free end and the substrate caused by the contact between the projection and the substrate can be prevented. Further, since the projection absorbs the overshoot energy, a time period for attenuating the overshoot can be shortened.
Further, the movable member may have a parallel portion parallel with the wall surface of the substrate which constitutes the lower wall surface of the flow path, and an upper portion inclined from the parallel portion toward the upper wall surface. In this case, when the protruded height is about 20 xcexcm, the first clearance may be within a range from 10 xcexcm to 15 xcexcm. By selecting the configuration of the movable member in this way, since an adequate sectional area of the flow path at the upstream side of the movable member is maintained, resistance of the flow path at the upstream side of the movable member during the re-filling can be reduced, thereby enhancing the re-filling efficiency. Further, since the free end of the movable member has the configuration inclined obliquely and upwardly, the damage of the free end of the movable member or the substrate due to the contact between the free end and the substrate during the overshooting can be prevented.
Further, the discharge port of the liquid discharge head according to the present invention may be provided above the heat generating body. In this case, a plurality of movable members are formed with respect to one heat generating body, and the plurality of movable members may be located symmetrically with respect to a bubbling center of the heat generating body.
A recording apparatus according to the present invention has conveying means for conveying a recording medium, and holding means for holding the liquid discharge head according to the present invention for effecting recording on the recording medium by discharging the liquid and capable of reciprocally shifting in a direction transverse to a conveying direction of the recording medium.
Incidentally, terms xe2x80x9cupstream sidexe2x80x9d and xe2x80x9cdownstream sidexe2x80x9d used in this specification are expressed with respect to a flow direction of the liquid from a supply source of the liquid toward the discharge port through the bubble generating area (or movable member) or with respect to a structural direction.
Further, a term xe2x80x9cdownstream sidexe2x80x9d regarding the bubble itself means a downstream side as to the above-mentioned flow direction or the constructural direction with respect to the center of the bubble or a bubble generated at a downstream side of the center of the heat generating body. Similarly, a term xe2x80x9cupstream sidexe2x80x9d regarding the bubble itself means an upstream side as to the above-mentioned flow direction or the structural direction with respect to the center of the bubble or a bubble generated at an upstream side of the area center of the heat generating body.
Further, a term xe2x80x9ccontactxe2x80x9d between the movable member and the regulating portion used in this specification may be an adjacent condition therebetween with the inter position of the liquid of about several xcexcm or may be a direct contact condition therebetween.